KR20230047932A - Negative electrode composition, negative electrode for lithium secondary battery comprising same, lithium secondary battery comprising negative electrode, and method for preparing negative electrode - Google Patents

Abstract

The present invention relates to a negative electrode composition, a negative electrode for a lithium secondary battery including the same, a lithium secondary battery including the negative electrode, and a method for manufacturing the negative electrode composition. The negative electrode composition includes: a silicon-based active material; a negative electrode conductive material; and a negative electrode binder. The present invention improves performance, such as securing a conductive path, by strengthening bonding within the negative electrode composition.

Description

Negative composition, a negative electrode for a lithium secondary battery including the same, a lithium secondary battery including the negative electrode, and a method for manufacturing the negative electrode composition ELECTRODE}

This application claims the benefit of the filing date of Korean Patent Application No. 10-2021-0130945 filed with the Korean Intellectual Property Office on October 01, 2021, all of which are incorporated herein.

The present application relates to a negative electrode composition, a negative electrode for a lithium secondary battery including the negative electrode, a lithium secondary battery including the negative electrode, and a method for preparing the negative electrode composition.

Due to the rapid increase in the use of fossil fuels, the demand for the use of alternative energy or clean energy is increasing, and as part of this, the most actively researched fields are power generation and storage using electrochemical reactions.

Currently, a secondary battery is a representative example of an electrochemical device using such electrochemical energy, and its use area is gradually expanding.

As technology development and demand for mobile devices increase, demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, lithium secondary batteries having high energy density and voltage, long cycle life, and low self-discharge rate have been commercialized and widely used. In addition, as an electrode for such a high-capacity lithium secondary battery, research is being actively conducted on a method for manufacturing a high-density electrode having a higher energy density per unit volume.

In general, a secondary battery is composed of an anode, a cathode, an electrolyte, and a separator. The negative electrode includes a negative electrode active material for intercalating and deintercalating lithium ions from the positive electrode, and silicon-based particles having a high discharge capacity may be used as the negative electrode active material.

In particular, in accordance with the recent demand for high-density energy batteries, research on how to increase capacity by using silicon-based compounds such as Si/C or SiOx, which have more than 10 times higher capacity than graphite-based materials as negative electrode active materials, is being actively conducted. However, in the case of a high-capacity material, a silicon-based compound has a higher capacity than conventionally used graphite, but has a problem in that the volume expands rapidly during the charging process and the conductive path is disconnected, thereby degrading battery characteristics.

Therefore, in order to solve the problem of using a silicon-based compound as an anode active material, volume expansion itself is suppressed, such as a method of adjusting the driving potential, a method of additionally coating a thin film on the active material layer, and a method of controlling the particle diameter of the silicon-based compound. Various methods for preventing or preventing the conductive path from being disconnected are being discussed, but in the case of the above methods, the performance of the battery may be deteriorated, so there is a limit to the application, and a negative electrode battery with a high silicon-based compound content is still Commercialization of manufacturing has limitations.

In addition, in the case of a negative electrode including a silicon-based active material, volume expansion is greater than that of a negative electrode including a carbon-based active material, so that it is difficult to secure a conductive path during charging and discharging.

Therefore, even when a silicon-based compound is used as an active material to improve capacity performance, research into a conductive material capable of preventing damage to a conductive path due to volume expansion of the silicon-based compound is required.

Japanese Unexamined Patent Publication No. 2009-080971

The silicon-based negative electrode has a high ratio of aqueous binder, which makes it easier to disperse the conductive material compared to the carbon-based negative electrode. Therefore, when the functional group content of the point-type conductive material used is adjusted by increasing the functional group content for dispersion and used together with the planar conductive material, It has been found that problems such as gas generation and securing of a conductive path can be solved with improved acidity.

Accordingly, the present application relates to a negative electrode composition, a negative electrode for a lithium secondary battery including the negative electrode, a lithium secondary battery including the negative electrode, and a method for preparing the negative electrode composition.

An exemplary embodiment of the present specification is a silicon-based active material; cathode conductive material; and a negative electrode binder, wherein the negative electrode conductive material includes a dotted conductive material and a plate-shaped conductive material, wherein the dotted conductive material has a volatile matter of 0.01% or more and less than 0.05%, and the silicon-based active material is the negative electrode. It provides a negative electrode composition that is 60 parts by weight or more based on 100 parts by weight of the composition.

In another exemplary embodiment, a dotted conductive material; and a binder to form a mixture; first mixing by adding water to the mixture; And a second mixing step by adding a silicon-based active material to the mixed mixture; forming the mixture; or further comprising a plate-like conductive material in the second mixing step, wherein the point-like conductive material has a volatile matter of 0.01% or more and less than 0.05%. do.

In another exemplary embodiment, a negative electrode current collector layer; and a negative electrode active material layer including the negative electrode composition according to the present application formed on one side or both sides of the negative electrode current collector layer.

Finally, the anode; A negative electrode for a lithium secondary battery according to the present application; a separator provided between the anode and the cathode; And an electrolyte; it provides a lithium secondary battery comprising a.

In the case of the negative electrode composition according to an exemplary embodiment of the present invention, in using a silicon-based active material, which is a high-capacity material, to manufacture a high-capacity battery, the negative electrode conductive material includes a dotted conductive material and a plate-shaped conductive material, and the dotted conductive material has a functional group content ( Volatile matter) satisfies 0.01% or more and less than 0.05%, it does not significantly affect the lifespan characteristics of existing lithium secondary batteries, and has excellent output characteristics at high C-rates as there are many points available for charging and discharging. .

In the case of point-type conductive materials used as conventional carbon-based anodes, they are generally hydrophobic and therefore difficult to disperse in water. As a result, intimacy in water increased and dispersibility improved, but a problem of gas generation due to side reactions occurred due to many functional groups. However, the negative electrode composition according to one embodiment of the present invention is applied to a silicon-based negative electrode, has a high binder ratio, and is easy to disperse compared to conventional carbon-based negative electrodes, and is a point-like conductive material with a functional group content of 0.01% or more and less than 0.05%. By using it, the functional group content is low and the hydrophobicity is strong, resulting in an increase in the strength of the composite with the surrounding conductive material and binder.

That is, in the case of the negative electrode composition according to one embodiment of the present invention, in using a silicon-based active material, which is a high-capacity material, to manufacture a high-capacity battery, the percentage of the aqueous binder is higher than that of the conventional carbon-based negative electrode, and the point-shaped conductive material has a functional group. A hydrophobic conductive material with a volatile matter content of 0.01% or more and less than 0.05% can be applied, and as a result, the bonding strength with the conductive material/binder located around it is improved, even if expansion occurs during charging / discharging of the Si-based negative electrode, the negative electrode The main feature is to improve performance such as securing a conductive path by strengthening the bonding in the composition.

In addition, when a conventional silicon-based active material is used, volume expansion during charging and discharging can also be minimized by using the negative electrode composition according to the present invention.

1 is a diagram showing a laminated structure of a negative electrode for a lithium secondary battery according to an exemplary embodiment of the present application.
2 is a diagram showing a laminated structure of a lithium secondary battery according to an exemplary embodiment of the present application.

Before describing the present invention, some terms are first defined.

In the present specification, when a part "includes" a certain component, it means that it may further include other components, not excluding other components unless otherwise stated.

In the present specification, 'p to q' means a range of 'p or more and q or less'.

In this specification, "specific surface area" is measured by the BET method, and is specifically calculated from the nitrogen gas adsorption amount under liquid nitrogen temperature (77K) using BELSORP-mino II of BEL Japan. That is, in the present application, the BET specific surface area may mean the specific surface area measured by the above measuring method.

In the present specification, "Dn" means the average particle diameter, and means the particle diameter at the n% point of the cumulative distribution of the number of particles according to the particle diameter. That is, D50 is the particle size at the 50% point of the cumulative distribution of the number of particles according to the particle size, D90 is the particle size at the 90% point of the cumulative distribution of the number of particles according to the particle size, and D10 is the 10% of the cumulative distribution of the number of particles according to the particle size. is the particle diameter at the point. Meanwhile, the average particle diameter can be measured using a laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (e.g. Microtrac S3500) to measure the difference in diffraction pattern according to the particle size when the particles pass through the laser beam to distribute the particle size. yields

In the present specification, the meaning that a polymer includes a certain monomer as a monomer unit means that the monomer participates in a polymerization reaction and is included as a repeating unit in the polymer. In the present specification, when a polymer includes a monomer, this is interpreted as the same as that the polymer includes a monomer as a monomer unit.

In the present specification, it is understood that the term 'polymer' is used in a broad sense including a copolymer unless otherwise specified as 'a homopolymer'.

In the present specification, the weight average molecular weight (Mw) and the number average molecular weight (Mn) are measured using a commercially available monodisperse polystyrene polymer (standard sample) of various degrees of polymerization for molecular weight measurement as a standard material, and gel permeation chromatography (Gel Permeation It is the molecular weight in terms of polystyrene measured by chromatography; GPC). In this specification, molecular weight means a weight average molecular weight unless otherwise specified.

Hereinafter, it will be described in detail with reference to the drawings so that those skilled in the art can easily practice the present invention. However, the present invention may be embodied in many different forms and is not limited to the description below.

An exemplary embodiment of the present specification is a silicon-based active material; cathode conductive material; and a negative electrode binder, wherein the negative electrode conductive material includes a dotted conductive material and a plate-shaped conductive material, wherein the dotted conductive material has a volatile matter of 0.01% or more and less than 0.05%, and the silicon-based active material is the negative electrode. It provides a negative electrode composition that is 60 parts by weight or more based on 100 parts by weight of the composition.

In the case of the negative electrode composition according to an exemplary embodiment of the present invention, in using a silicon-based active material, which is a high-capacity material, to manufacture a high-capacity battery, the point-like conductive material has a high functional group content compared to the case of using a conventional carbon-based negative electrode. A hydrophobic conductive material having a volatile matter of 0.01% or more and less than 0.05% can be applied, and as a result, the bonding strength with the conductive material / binder located nearby is improved, even if expansion occurs during charging / discharging of the Si-based negative electrode, negative electrode composition Its main feature is to improve performance, such as securing a conductive path by strengthening the coupling inside.

In one embodiment of the present application, the functional group content (Volatile matter) is a numerical expression of the functional group content included in the conductive material, which can be calculated as a weight loss rate as follows.

Weight loss rate = [(weight of material before heat treatment - weight of material after heat treatment)/weight of material before heat treatment]Х100

The amount lost by the heat treatment may be a functional group present on the surface of the material before the heat treatment. The functional group may be at least one functional group selected from the group consisting of a hydroxy group, a carboxy group, an aldehyde group, a phenol group, a ketone group, an anhydride group, a lactone group, a peroxide group, an ether group, a hemiacetal group, a quinone group, and an amine group. there is.

The functional group content (Volatile matter) according to the present application used an analysis method that can confirm the mass while raising the temperature using thermal analysis. It can be measured by a method of confirming the amount of the compound volatilized by raising the temperature to , and the analyzed amount can be expressed as the content of functional groups present on the surface of the point-shaped conductive material.

In one embodiment of the present application, the silicon-based active material is a negative electrode composition comprising at least one selected from the group consisting of SiOx (x=0), SiOx (0<x<2), SiC, and Si alloys to provide.

In an exemplary embodiment of the present application, the silicon-based active material includes at least one selected from the group consisting of SiOx (x=0), SiOx (0<x<2), and metal impurities, based on 100 parts by weight of the silicon-based active material. It provides a negative electrode composition comprising 70 parts by weight or more of the SiOx (x = 0).

In another embodiment, based on 100 parts by weight of the silicon-based active material, the SiOx (x = 0) may include 70 parts by weight or more, preferably 80 parts by weight or more, and more preferably 90 parts by weight or more, 100 parts by weight or less, preferably 99 parts by weight or less, more preferably 95 parts by weight or less.

In one embodiment of the present application, the silicon-based active material may use pure silicon (Si) as the silicon-based active material. The use of pure silicon (Si) as a silicon-based active material means that, based on 100 parts by weight of the total silicon-based active material as described above, pure Si particles (SiOx (x = 0)) not bonded to other particles or elements are within the above range. It can mean including.

In the case of silicon-based active materials, compared to graphite-based active materials used in the past, attempts to apply them are increasing due to their significantly higher capacity, but their volume expansion rate is high during charging and discharging. there is.

Therefore, in the case of the present invention, in order to solve the above problems, while using only a silicon-based active material as an anode active material for improving capacity performance and high energy density, a dotted conductive material and a plate-shaped conductive material are included as a negative electrode conductive material, and a functional group The existing problem was solved by using a volatile matter of 0.01% or more and less than 0.05%.

Meanwhile, the average particle diameter (D50) of the silicon-based active material of the present invention may be 5 μm to 10 μm, specifically 5.5 μm to 8 μm, and more specifically 6 μm to 7 μm. When the average particle diameter is less than 5 μm, the specific surface area of the particles is excessively increased, and thus the viscosity of the negative electrode slurry is excessively increased. Accordingly, the dispersion of the particles constituting the negative electrode slurry is not smooth. In addition, when the size of the silicon-based active material is too small, the contact area of the silicon particles and the conductive material is reduced by the composite of the conductive material and the binder in the negative electrode slurry, so the possibility of disconnection of the conductive network increases, resulting in a decrease in capacity retention rate. On the other hand, when the average particle diameter exceeds 10 μm, excessively large silicon particles exist, resulting in an uneven surface of the negative electrode, resulting in non-uniformity in current density during charging and discharging. In addition, when the silicon particles are too large, the phase stability of the negative electrode slurry becomes unstable, resulting in a decrease in processability. Accordingly, the capacity retention rate of the battery is lowered.

In one embodiment of the present application, the silicon-based active material generally has a characteristic BET surface area. The BET surface area of the silicon-based active material is preferably 0.01 m ² /g to 150.0 m ² /g, more preferably 0.1 m ² /g to 100.0 m ² /g, particularly preferably 0.2 m ² /g to 80.0 m ² /g, most preferably from 0.2 m ² /g to 18.0 m ² /g. The BET surface area is measured according to DIN 66131 (using nitrogen).

In one embodiment of the present application, the silicon-based active material may exist, for example, in a crystalline or amorphous form, and is preferably not porous. The silicon particles are preferably spherical or fragment-shaped particles. Alternatively but less preferably, the silicon particles may also have a fibrous structure or be present in the form of a silicon-comprising film or coating.

In one embodiment of the present application, the silicon-based active material provides a negative electrode composition that is 60 parts by weight or more based on 100 parts by weight of the negative electrode composition.

In another exemplary embodiment, the silicon-based active material may include 60 parts by weight or more, preferably 65 parts by weight or more, more preferably 70 parts by weight or more, based on 100 parts by weight of the negative electrode composition, and 95 parts by weight or less , preferably 90 parts by weight or less, more preferably 80 parts by weight or less.

The negative electrode composition according to the present application uses a specific negative electrode conductive material and negative electrode binder that can control the volume expansion rate during charging and discharging even when a silicon-based active material having a significantly high capacity is used in the above range, and the negative electrode composition includes the above range. It does not degrade the performance and has excellent output characteristics in charging and discharging.

In one embodiment of the present application, the silicon-based active material may have a non-spherical shape and its sphericity is, for example, 0.9 or less, for example, 0.7 to 0.9, for example 0.8 to 0.9, for example 0.85 to 0.9 am.

In the present application, the circularity (circularity) is determined by the following formula 1, A is the area, P is the boundary line.

[Equation 1]

4πA/ ^P2

In the past, it was common to use only graphite-based compounds as negative electrode active materials, but recently, as the demand for high-capacity batteries has increased, attempts to mix and use silicon-based compounds in order to increase capacity are increasing. However, in the case of silicon-based compounds, there is a limit in that the volume rapidly expands during the charge/discharge process, damaging the conductive path formed in the negative electrode active material layer, thereby degrading the performance of the battery.

Therefore, in one embodiment of the present application, the negative electrode conductive material includes a dot-like conductive material and a plate-like conductive material, and the dot-like conductive material has a volatile matter of 0.01% or more and less than 0.05%. Even when the silicon-based active material is expanded using the conductive material, since the conductive material can be constantly positioned on the surface of the particles, between the particles, and between the particle agglomerates, the conductive path formed by the conductive material is not affected by volume expansion, so the battery can keep the performance of

In one embodiment of the present application, the dotted conductive material may be used to improve conductivity of the negative electrode, and refers to a dotted or spherical conductive material having conductivity without causing chemical change. Specifically, the point-shaped conductive material is natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, channel black, farnes black, lamp black, thermal black, conductive fiber, fluorocarbon, aluminum powder, nickel powder, zinc oxide, It may be at least one selected from the group consisting of potassium titanate, titanium oxide, and polyphenylene derivatives, and may preferably include carbon black in terms of high conductivity and excellent dispersibility.

In an exemplary embodiment of the present application, the point-shaped conductive material may have a BET specific surface area of 40 m ² /g or more and 70 m ² /g or less, preferably 45 m ² /g or more and 65 m ² /g or less, more preferably 50 m 2 / ^{g or less} . /g or more and 60 m ² /g or less.

In one embodiment of the present application, the point-like conductive material may satisfy a functional group content (Volatile matter) of 0.01% or more and less than 0.05%, preferably 0.01% or more and 0.04% or less, more preferably 0.01% or more and 0.03% or less. there is.

In particular, when the functional group content of the dotted conductive material satisfies the above range, functional groups present on the surface of the dotted conductive material exist, so that the dotted conductive material can be smoothly dispersed in the solvent when water is used as a solvent. In particular, in the present invention, the functional group content of the point-like conductive material can be lowered by using a silicon-based active material and a specific binder (mainly an aqueous binder), thereby having an excellent effect in improving dispersibility.

In one embodiment of the present application, it is characterized in that it includes a silicon-based active material and a dotted conductive material having a functional group content within the above range, the control of the functional group content can be adjusted according to the degree of heat treatment of the dotted conductive material there is.

That is, in the production of the point-like conductive material, a high functional group content means a lot of foreign substances, and a low functional group content means more heat treatment processing, and the point-like conductive material according to the present application has a functional group content within the above range. In order to satisfy, it is characterized in that the point-shaped conductive material is subjected to a certain portion of heat treatment to satisfy the functional group content range.

Specifically, as the dispersibility of the point-like conductive material is improved, even if the content of the point-like conductive material is increased in the negative electrode slurry having the same solid content, the viscosity of the negative electrode slurry can be maintained at an appropriate level, maintaining a stable state of fairness The uniformity of the formed cathode can be improved.

In one embodiment of the present application, the particle diameter of the dotted conductive material may be 10 nm to 100 nm, preferably 20 nm to 90 nm, and more preferably 20 nm to 60 nm.

In one embodiment of the present application, the negative electrode conductive material may include a plate-shaped conductive material.

The plate-shaped conductive material may serve to improve conductivity by increasing surface contact between silicon particles in the negative electrode, and at the same time suppress disconnection of the conductive path due to volume expansion. The plate-shaped conductive material may be expressed as a planar conductive material or a bulk type conductive material.

In an exemplary embodiment of the present application, the plate-like conductive material may include at least one selected from the group consisting of plate-like graphite, graphene, graphene oxide, and graphite flakes, and preferably may be plate-like graphite.

In one embodiment of the present application, the planar conductive material may be provided in a form bonded to the surface of the silicon-based particle. Specifically, the -OH group or -O on the surface of the silicon-based particle may be provided in a form in which the hydrophilic group of the planar conductive material is bonded to each other.

In one embodiment of the present application, the average particle diameter (D50) of the plate-shaped conductive material may be 2 μm to 7 μm, specifically 3 μm to 6 μm, and more specifically 4 μm to 5 μm. . When the above range is satisfied, dispersion is easy without causing an excessive increase in viscosity of the negative electrode slurry based on a sufficient particle size. Therefore, the dispersion effect is excellent when dispersing using the same equipment and time.

In one embodiment of the present application, the plate-shaped conductive material provides a negative electrode composition in which D10 is 0.5 μm or more and 1.5 μm or less, D50 is 2.5 μm or more and 3.5 μm or less, and D90 is 7.0 μm or more and 15.0 μm or less.

In one embodiment of the present application, the plate-shaped conductive material is a high specific surface area plate-shaped conductive material having a high BET specific surface area; Alternatively, a plate-shaped conductive material having a low specific surface area may be used.

In one embodiment of the present application, the plate-shaped conductive material is a high specific surface area plate-shaped conductive material; Alternatively, a plate-shaped conductive material with a low specific surface area can be used without limitation, but in particular, the plate-shaped conductive material according to the present application can be affected to some extent in the electrode performance by the dispersion effect, so that the plate-shaped conductive material with a low specific surface area that does not cause a problem in dispersion is used. may be particularly desirable.

In one embodiment of the present application, the plate-shaped conductive material may have a BET specific surface area of 1 m ² /g or more.

In another exemplary embodiment, the plate-shaped conductive material may have a BET specific surface area of 1 m ² /g or more and 500 m ² /g or less, preferably 5 m ² /g or more and 300 m ² /g or less, more preferably 5 m ^{2 /g} or more. g or more and 300 m ² /g or less.

In another embodiment, the plate-like conductive material is a plate-like conductive material with a high specific surface area, and the BET specific surface area is 50 m ² /g or more and 500 m ² /g or less, preferably 80 m ² /g or more and 300 m ² /g or less, more preferably Preferably, a range of 100 m ² /g or more and 300 m ² /g or less may be satisfied.

In another embodiment, the plate-shaped conductive material is a plate-shaped conductive material with a low specific surface area, and the BET specific surface area is 1 m ² /g or more and 40 m ² /g or less, preferably 5 m ² /g or more and 30 m ² /g or less, more preferably Preferably, a range of 5 m ² /g or more and 25 m ² /g or less may be satisfied.

Other negative electrode conductive materials may include linear conductive materials such as carbon nanotubes. Carbon nanotubes may be bundled carbon nanotubes. The bundled carbon nanotubes may include a plurality of carbon nanotube units. Specifically, the term 'bundle type' herein means, unless otherwise specified, a bundle in which a plurality of carbon nanotube units are arranged side by side or entangled in substantially the same orientation with axes in the longitudinal direction of the carbon nanotube units. It refers to a secondary shape in the form of a bundle or rope. The carbon nanotube unit has a graphite sheet having a cylindrical shape with a nano-sized diameter and an sp2 bonding structure. At this time, the characteristics of a conductor or a semiconductor may be exhibited according to the angle and structure of the graphite surface being rolled. Compared to entangled carbon nanotubes, the bundled carbon nanotubes can be uniformly dispersed during manufacturing of the negative electrode, and the conductivity of the negative electrode can be improved by smoothly forming a conductive network in the negative electrode.

However, in the present invention, the output characteristics of the secondary battery of the present invention are improved by including point-shaped and plate-shaped conductive materials as the conductive material and adjusting the functional group content of the point-shaped conductive material without using the linear conductive material as described above. do.

In an exemplary embodiment of the present application, the negative electrode conductive material is provided in an amount of 10 parts by weight or more and 40 parts by weight or less based on 100 parts by weight of the negative electrode composition.

In another embodiment, the negative electrode conductive material is 10 parts by weight or more and 40 parts by weight or less, preferably 10 parts by weight or more and 30 parts by weight or less, more preferably 15 parts by weight or more and 25 parts by weight based on 100 parts by weight of the negative electrode composition. May include the following.

In one embodiment of the present application, 45 to 60 parts by weight of the point-shaped conductive material based on 100 parts by weight of the negative electrode conductive material; And it provides a negative electrode composition comprising 40 to 55 parts by weight of the plate-shaped conductive material.

In another exemplary embodiment, 45 to 60 parts by weight, preferably 47 to 58 parts by weight, and more preferably 50 to 55 parts by weight of the point-shaped conductive material may be included based on 100 parts by weight of the negative electrode conductive material.

In another exemplary embodiment, 40 to 55 parts by weight of the plate-shaped conductive material, preferably 42 to 53 parts by weight, and more preferably 45 to 50 parts by weight, based on 100 parts by weight of the negative electrode conductive material.

In one embodiment of the present application, the negative electrode conductive material includes a dot-shaped conductive material and a plate-shaped conductive material, and a ratio of the dot-shaped conductive material to the plate-shaped conductive material may satisfy 1:0.8 to 1:1.2.

In one embodiment of the present application, the ratio of the dot-shaped conductive material to the plate-shaped conductive material may satisfy 1:1.

In one embodiment of the present application, as the negative electrode conductive material includes a dotted conductive material and a plate-shaped conductive material and satisfies the composition and ratio, respectively, it does not significantly affect the lifespan characteristics of an existing lithium secondary battery, and charge and discharge As the number of possible points increases, output characteristics are excellent at a high C-rate.

Since the continuous breaking of the active material due to the volume expansion/contraction of silicon and the occurrence of conductive short-circuits due to breakage of particles are the biggest cause of deterioration in performance, in constructing an electrode containing a silicon-based active material, rather than improving the performance of the silicon-based electrode, The most important factor is how to maintain the condition for a long time.

In order to solve the above problem, a variety of cathode conductive materials are used. In general, carbon black/plate-shaped/CNT series are mainly used, and a network is used using a cathode conductive material that connects various intervals according to the size and aspect ratio of particles. composed of

The negative electrode conductive material according to the present application includes two types of a dot-shaped conductive material and a plate-shaped conductive material having the above characteristics. If the plate-shaped conductive material is not included, the active material is formed at intervals in which the conductive network cannot be maintained in irregularly expanding/contracting silicon particles. A short circuit occurs, which causes performance deterioration. In the case of plate-shaped conductive materials, since most of them use graphite materials, they have an advantage in that they have fewer side reactions than point-type conductive materials, and unlike point-type conductive materials, some charge/discharge is possible, so Li It is more efficient than using a dotted conductive material alone in moving ions to the surroundings. That is, when the plate-shaped conductive material is not used, it shows deterioration. The main feature of the present invention is to solve the problem of the silicon-based active material by including two types of a specific dot-shaped conductive material and a plate-shaped conductive material.

In the case of the negative electrode conductive material according to the present application, it has a completely different configuration from the conductive material applied to the positive electrode. That is, in the case of the anode conductive material according to the present application, it serves to hold the contact between silicon-based active materials whose volume expansion of the electrode is very large due to charging and discharging. As a role of imparting, its composition and role are completely different from those of the negative electrode conductive material of the present invention.

In addition, the negative electrode conductive material according to the present application is applied to a silicon-based active material, and has a completely different configuration from that of a conductive material applied to a graphite-based active material. That is, since the conductive material used in the electrode having the graphite-based active material simply has smaller particles than the active material, it has characteristics of improving output characteristics and imparting some conductivity, unlike the negative electrode conductive material applied together with the silicon-based active material as in the present invention. The composition and role are completely different.

In one embodiment of the present application, the plate-shaped conductive material used as the negative electrode conductive material described above has a different structure and role from the carbon-based active material generally used as the negative electrode active material. Specifically, the carbon-based active material used as the negative electrode active material may be artificial graphite or natural graphite, and refers to a material processed into a spherical or dotted shape to facilitate storage and release of lithium ions.

On the other hand, the plate-shaped conductive material used as the negative electrode conductive material is a material having a plane or plate shape, and may be expressed as plate-shaped graphite. That is, as a material included to maintain a conductive path in the negative active material layer, it means a material used to secure a conductive path in a planar shape inside the negative active material layer, rather than playing a role in storing and releasing lithium.

That is, in the present application, the fact that plate-like graphite is used as a conductive material means that it is processed into a planar or plate-like shape and used as a material that secures a conductive path rather than a role of storing or releasing lithium. At this time, the negative active material included together has high capacity characteristics for storing and releasing lithium, and serves to store and release all lithium ions transferred from the positive electrode.

On the other hand, in the present application, the use of a carbon-based active material as an active material means that it is processed into a point shape or sphere and used as a material that stores or releases lithium.

In one embodiment of the present application, the negative electrode binder is polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidenefluoride, polyacrylonitrile, Polymethylmethacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene -Selected from the group consisting of propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, polyacrylic acid, and materials in which hydrogen is substituted with Li, Na or Ca, etc. It may include at least one that is, and may also include various copolymers thereof.

The negative electrode binder according to an exemplary embodiment of the present application serves to hold the silicon-based active material and the negative electrode conductive material in order to prevent distortion and structural deformation of the negative electrode structure in volume expansion and relaxation of the silicon-based active material, and satisfies the above role. When all general anode binders can be applied, a water-based binder can be used specifically, and a PAM-based binder can be used more specifically.

In one embodiment of the present application, the negative electrode binder may include 30 parts by weight or less, preferably 25 parts by weight or less, more preferably 20 parts by weight or less, and 5 parts by weight or more based on 100 parts by weight of the negative electrode composition. , 10 parts by weight or more.

Compared to conventional carbon-based anodes, when Si-based anodes are used, a water-based binder is applied in the above weight part to use a point-type conductive material having a low functional group content. It has a characteristic that the bonding strength is excellent.

In one embodiment of the present application, a dotted conductive material; and a negative electrode binder to form a mixture; first mixing by adding water to the mixture; And a second mixing step by adding a silicon-based active material to the mixed mixture; forming the mixture; or further comprising a plate-like conductive material in the second mixing step, wherein the point-like conductive material has a volatile matter of 0.01% or more and less than 0.05%. do.

In the preparation method of the negative electrode composition, each composition included in the negative electrode composition may be the same as described above.

In an exemplary embodiment of the present application, the first mixing and the second mixing step is mixing at 2,000 rpm to 3,000 rpm for 10 minutes to 60 minutes.

In one embodiment of the present application, the negative electrode may form a negative electrode for a lithium secondary battery by coating one or both surfaces of a current collector with a negative electrode slurry containing the negative electrode composition.

In one embodiment of the present application, the negative electrode slurry includes a negative electrode composition; And a slurry solvent; may include.

In one embodiment of the present application, the solid content of the negative electrode slurry may satisfy 5% or more and 40% or less.

In another exemplary embodiment, the solid content of the negative electrode slurry may satisfy a range of 5% or more and 40% or less, preferably 7% or more and 35% or less, and more preferably 10% or more and 30% or less.

The solids content of the negative electrode slurry may refer to the content of the negative electrode composition included in the negative electrode slurry, and may refer to the content of the negative electrode composition based on 100 parts by weight of the negative electrode slurry.

When the solids content of the negative electrode slurry satisfies the above range, the negative electrode active material layer can be efficiently formed by minimizing particle aggregation of the negative electrode composition due to appropriate viscosity when forming the negative electrode active material layer.

In one embodiment of the present application, the slurry solvent may be used without limitation as long as it can disperse the above-described negative electrode composition, but may specifically use water or NMP.

In one embodiment of the present application, the negative current collector layer; and a negative electrode active material layer including the negative electrode composition according to the present application formed on one side or both sides of the negative electrode current collector layer.

1 is a diagram showing a laminated structure of a negative electrode for a lithium secondary battery according to an exemplary embodiment of the present application. Specifically, the negative electrode 100 for a lithium secondary battery including the negative electrode active material layer 20 on one surface of the negative electrode current collector layer 10 can be confirmed, and FIG. 1 shows that the negative electrode active material layer is formed on one surface, but the negative electrode collector It can be included on both sides of the entire layer.

In one embodiment of the present application, the negative current collector layer generally has a thickness of 1 μm to 100 μm. Such an anode current collector layer is not particularly limited as long as it does not cause chemical change in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, copper or stainless steel. A surface treated with carbon, nickel, titanium, silver, or the like, an aluminum-cadmium alloy, or the like may be used. In addition, fine irregularities may be formed on the surface to enhance the bonding strength of the negative active material, and may be used in various forms such as films, sheets, foils, nets, porous materials, foams, and nonwoven fabrics.

In one embodiment of the present application, the negative electrode current collector layer has a thickness of 1 μm or more and 100 μm or less, and the negative electrode active material layer has a thickness of 20 μm or more and 500 μm or less.

However, the thickness may be variously modified depending on the type and purpose of the negative electrode used, but is not limited thereto.

In one embodiment of the present application, the porosity of the negative electrode active material layer may satisfy a range of 10% or more and 60% or less.

In another exemplary embodiment, the porosity of the negative electrode active material layer may satisfy a range of 10% or more and 60% or less, preferably 20% or more and 50% or less, and more preferably 30% or more and 45% or less.

The porosity is a silicon-based active material included in the negative electrode active material layer; conductive material; And as changed according to the composition and content of the binder, in particular, the silicon-based active material according to the present application; And it is characterized in that it satisfies the above range by including a specific composition and content of the conductive material, so that the electrode has an appropriate range of electrical conductivity and resistance.

In one embodiment of the present application, the anode; A negative electrode for a lithium secondary battery according to the present application; a separator provided between the anode and the cathode; And an electrolyte; it provides a lithium secondary battery comprising a.

2 is a diagram showing a laminated structure of a lithium secondary battery according to an exemplary embodiment of the present application. Specifically, the negative electrode 100 for a lithium secondary battery including the negative electrode active material layer 20 on one surface of the negative electrode current collector layer 10 can be confirmed, and the positive electrode active material layer 40 on one surface of the positive electrode current collector layer 50 It can be seen that the positive electrode 200 for a lithium secondary battery including a, and the negative electrode 100 for a lithium secondary battery and the positive electrode 200 for a lithium secondary battery are formed in a laminated structure with a separator 30 interposed therebetween.

A secondary battery according to an exemplary embodiment of the present specification may include the anode for a lithium secondary battery described above. Specifically, the secondary battery may include a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, and the negative electrode is the same as the negative electrode described above. Since the cathode has been described above, a detailed description thereof will be omitted.

The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and including the positive electrode active material.

In the positive electrode, the positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or carbon on the surface of aluminum or stainless steel. , those surface-treated with nickel, titanium, silver, etc. may be used. In addition, the cathode current collector may have a thickness of typically 3 to 500 μm, and adhesion of the cathode active material may be increased by forming fine irregularities on the surface of the current collector. For example, it may be used in various forms such as films, sheets, foils, nets, porous materials, foams, and non-woven fabrics.

The cathode active material may be a commonly used cathode active material. Specifically, the cathode active material may include layered compounds such as lithium cobalt oxide (LiCoO ₂ ) and lithium nickel oxide (LiNiO ₂ ), or compounds substituted with one or more transition metals; lithium iron oxides such as LiFe ₃ O ₄ ; lithium manganese oxides such as Li _1+c1 Mn _2-c1 O ₄ (0≤c1≤0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ ; lithium copper oxide (Li ₂ CuO ₂ ); vanadium oxides such as LiV ₃ O ₈ , V ₂ O ₅ , and Cu ₂ V ₂ O ₇ ; Represented by the formula LiNi _1-c2 M _c2 O ₂ (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and satisfies 0.01≤c2≤0.6) Ni site-type lithium nickel oxide; Formula LiMn _2-c3 M _c3 O ₂ (wherein M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01≤c3≤0.6) or Li ₂ Mn ₃ MO ₈ (here, M is at least one selected from the group consisting of Fe, Co, Ni, Cu and Zn.) Lithium manganese composite oxide represented by; Examples include LiMn ₂ O ₄ in which Li in the formula is partially substituted with an alkaline earth metal ion, but is not limited thereto. The anode may be Li-metal.

In an exemplary embodiment of the present application, the positive electrode active material includes a lithium composite transition metal compound including nickel (Ni), cobalt (Co), and manganese (Mn), and the lithium composite transition metal compound is a single particle or a secondary particle. Including, the average particle diameter (D50) of the single particles may be 1㎛ or more.

For example, the average particle diameter (D50) of the single particles is 1 μm or more and 12 μm or less, 1 μm or more and 8 μm or less, 1 μm or more and 6 μm or less, 1 μm or more and 12 μm or less, 1 μm or more and 8 μm or less, or 1 μm. It may be more than 6 μm or less.

Even if the single particle is formed with a small average particle diameter (D50) of 1 μm or more and 12 μm or less, the particle strength may be excellent. For example, the single particle may have a particle strength of 100 to 300 MPa when rolling with a force of 650 kgf/cm ² . Accordingly, even if the single particle is rolled with a strong force of 650 kgf/cm ² , the phenomenon of increasing fine particles in the electrode due to particle breakage is alleviated, thereby improving the lifespan characteristics of the battery.

The single particle may be prepared by mixing and calcining a transition metal precursor and a lithium source material. The secondary particles may be prepared in a different way from the single particles, and their composition may be the same as or different from that of the single particles.

The method of forming the single particles is not particularly limited, but generally can be formed by underfiring by raising the firing temperature, using additives such as grain growth promoters that help underfiring, or by changing the starting material. can be manufactured

For example, the firing is performed at a temperature capable of forming single particles. In order to form it, firing should be performed at a temperature higher than that of the secondary particles, for example, if the composition of the precursor is the same, firing should be performed at a temperature about 30° C. to 100° C. higher than that of the secondary particles. The firing temperature for forming the single particle may vary depending on the metal composition in the precursor. For example, a high-Ni NCM-based lithium composite transition metal oxide having a nickel (Ni) content of 80 mol% or more is used. In the case of forming single particles, the firing temperature may be about 700°C to 1000°C, preferably about 800°C to 950°C. When the sintering temperature satisfies the above range, a cathode active material including single particles having excellent electrochemical properties may be prepared. If the firing temperature is less than 790 ° C, a cathode active material containing a lithium complex transition metal compound in the form of secondary particles can be prepared, and if it exceeds 950 ° C, excessive firing occurs and the layered crystal structure is not properly formed, resulting in electrochemical characteristics may deteriorate.

In the present specification, the single particle is a term used to distinguish from conventional secondary particles formed by aggregation of tens to hundreds of primary particles, and includes a single particle composed of one primary particle and 30 or less primary particles. It is a concept that includes pseudo-single-particle forms that are aggregates.

Specifically, in the present invention, the single particle may be in the form of a single particle composed of one primary particle or a quasi-single particle, which is an aggregate of 30 or less primary particles, and the secondary particle may be in the form of an aggregate of hundreds of primary particles. .

In one embodiment of the present application, the lithium composite transition metal compound, which is the cathode active material, further includes secondary particles, and the average particle diameter (D50) of the single particles is smaller than the average particle diameter (D50) of the secondary particles.

In the present invention, the single particle may be in the form of a single particle composed of one primary particle or a quasi-single particle, which is an aggregate of 30 or less primary particles, and the secondary particle may be in the form of an aggregate of hundreds of primary particles.

The above-described lithium composite transition metal compound may further include secondary particles. A secondary particle means a form formed by aggregation of primary particles, and can be distinguished from the concept of a single particle including one primary particle, one single particle, or a quasi-single particle form, which is an aggregate of 30 or less primary particles. .

The secondary particle may have a particle diameter (D50) of 1 μm to 20 μm, 2 μm to 17 μm, and preferably 3 μm to 15 μm. The specific surface area (BET) of the secondary particles may be 0.05 m ² /g to 10 m ² /g, preferably 0.1 m ² /g to 1 m ² /g, and more preferably 0.3 m ² /g to 0.8 m ² /g.

In a further exemplary embodiment of the present application, the secondary particles are aggregates of primary particles, and the average particle diameter (D50) of the primary particles is 0.5 μm to 3 μm. Specifically, the secondary particles may be in the form of an aggregate of hundreds of primary particles, and the average particle diameter (D50) of the primary particles may be 0.6 μm to 2.8 μm, 0.8 μm to 2.5 μm, or 0.8 μm to 1.5 μm. .

When the average particle diameter (D50) of the primary particles satisfies the above range, a single-particle cathode active material having excellent electrochemical properties may be formed. If the average particle diameter (D50) of the primary particles is too small, the number of agglomerations of the primary particles forming lithium nickel-based oxide particles increases, reducing the effect of suppressing particle breakage during rolling, and the average particle diameter (D50) of the primary particles is too small. If it is large, the lithium diffusion path inside the primary particle becomes long, and resistance may increase and output characteristics may deteriorate.

According to a further embodiment of the present application, the average particle diameter (D50) of the single particles is smaller than the average particle diameter (D50) of the secondary particles. As a result, even if the single particle is formed with a small particle diameter, the particle strength may be excellent, and as a result, the phenomenon of increasing fine particles in the electrode due to particle breakage is alleviated, thereby improving the lifespan characteristics of the battery.

In one embodiment of the present application, the average particle diameter (D50) of the single particles is smaller than the average particle diameter (D50) of the secondary particles by 1 μm to 18 μm.

For example, the average particle diameter (D50) of the single particles may be 1 μm to 16 μm smaller, 1.5 μm to 15 μm smaller, or 2 μm to 14 μm smaller than the average particle diameter (D50) of the secondary particles.

When the average particle diameter (D50) of the single particles is smaller than the average particle diameter (D50) of the secondary particles, for example, when the above range is satisfied, the single particles may have excellent particle strength even if they are formed with a small particle diameter, and thereby The phenomenon of increasing fine particles in the electrode due to cracking is alleviated, and there is an effect of improving the lifespan characteristics and energy density of the battery.

According to a further exemplary embodiment of the present application, the single particle is included in 15 parts by weight to 100 parts by weight based on 100 parts by weight of the positive electrode active material. The single particle may be included in an amount of 20 parts by weight to 100 parts by weight, or 30 parts by weight to 100 parts by weight based on 100 parts by weight of the cathode active material.

For example, the single particle may be included in an amount of 15 parts by weight or more, 20 parts by weight or more, 25 parts by weight or more, 30 parts by weight or more, 35 parts by weight or more, 40 parts by weight or more, or 45 parts by weight or more based on 100 parts by weight of the positive electrode active material. there is. The single particle may be included in an amount of 100 parts by weight or less based on 100 parts by weight of the positive electrode active material.

When the single particle within the above range is included, excellent battery characteristics may be exhibited in combination with the anode material described above. In particular, when the single particle is 15 parts by weight or more, the increase in fine particles in the electrode due to particle breakage during the rolling process after fabrication of the electrode can be alleviated, and thus the lifespan characteristics of the battery can be improved.

In an exemplary embodiment of the present application, the lithium composite transition metal compound may further include secondary particles, and the secondary particles may be 85 parts by weight or less based on 100 parts by weight of the positive electrode active material. The amount of the secondary particles may be 80 parts by weight or less, 75 parts by weight or less, or 70 parts by weight or less based on 100 parts by weight of the cathode active material. The secondary particles may be 0 parts by weight or more based on 100 parts by weight of the positive electrode active material.

When the above range is satisfied, the aforementioned effects due to the existence of single particles of the cathode active material may be maximized. In the case of including the secondary particle cathode active material, the component may be the same as those exemplified in the single-particle cathode active material described above, or may be other components, and may mean a form in which a single particle form is aggregated.

In one embodiment of the present application, the positive electrode active material in 100 parts by weight of the positive electrode active material layer is 80 parts by weight or more and 99.9 parts by weight or less, preferably 90 parts by weight or more and 99.9 parts by weight or less, more preferably 95 parts by weight or more and 99.9 parts by weight or less. parts or less, more preferably 98 parts by weight or more and 99.9 parts by weight or less.

The positive electrode active material layer may include a positive electrode conductive material and a positive electrode binder together with the positive electrode active material described above.

At this time, the positive electrode conductive material is used to impart conductivity to the electrode, and in the configured battery, any material that does not cause chemical change and has electronic conductivity can be used without particular limitation. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskeys such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like, and one of them alone or a mixture of two or more may be used.

In addition, the positive electrode binder serves to improve adhesion between particles of the positive electrode active material and adhesion between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC) ), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and the like may be used alone or in a mixture of two or more of them.

The separator separates the negative electrode and the positive electrode and provides a passage for the movement of lithium ions. If it is normally used as a separator in a secondary battery, it can be used without particular limitation. Excellent is desirable. Specifically, a porous polymer film, for example, a porous polymer film made of polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer, or these A laminated structure of two or more layers of may be used. In addition, conventional porous non-woven fabrics, for example, non-woven fabrics made of high-melting glass fibers, polyethylene terephthalate fibers, and the like may be used. In addition, a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may be selectively used in a single-layer or multi-layer structure.

Examples of the electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in manufacturing a lithium secondary battery.

Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

As the non-aqueous organic solvent, for example, N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyllolactone, 1,2-dimethine Toxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxorane, formamide, dimethylformamide, dioxorane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid Triester, trimethoxy methane, dioxolane derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl propionate, propionic acid An aprotic organic solvent such as ethyl may be used.

In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high-viscosity organic solvents and have a high dielectric constant, so they can be preferably used because they dissociate lithium salts well, and dimethyl carbonate and diethyl carbonate and When the same low-viscosity, low-dielectric constant linear carbonate is mixed and used in an appropriate ratio, an electrolyte having high electrical conductivity can be made and can be used more preferably.

The metal salt may be a lithium salt, and the lithium salt is a material that is soluble in the non-aqueous electrolyte. For example, the anion of the lithium salt is F ^- , Cl ^- , I ^- , NO ₃ ^- , N (CN ) ₂ ^- , BF ₄ ^- , ClO ₄ ^- , PF ₆ ^- , (CF ₃ ) ₂ PF ₄ ^- , (CF ₃ ) ₃ PF ₃ ^- , (CF ₃ ) ₄ PF ₂ ^- , (CF ₃ ) ₅ PF ^- , (CF ₃ ) ₆ P ^- , CF ₃ SO ₃ ^- , CF ₃ CF ₂ SO ₃ ^- , (CF ₃ SO ₂ ) ₂ N ^- , (FSO ₂ ) ₂ N ^- , CF ₃ CF ₂ (CF ₃ ) ₂ CO ^- , (CF ₃ SO ₂ ) ₂ CH ^- , (SF ₅ ) ₃ C ^- , (CF ₃ SO ₂ ) ₃ C ^- , CF ₃ (CF ₂ ) ₇ SO ₃ ^- , CF ₃ CO ₂ ^- , CH ₃ CO ₂ ^- , SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- At least one selected from the group consisting of may be used.

In addition to the above electrolyte components, the electrolyte may include, for example, haloalkylene carbonate-based compounds such as difluoroethylene carbonate, pyridine, and triglycerides for the purpose of improving battery life characteristics, suppressing battery capacity decrease, and improving battery discharge capacity. Ethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imida One or more additives such as zolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol or aluminum trichloride may be further included.

One embodiment of the present invention provides a battery module including the secondary battery as a unit cell and a battery pack including the same. Since the battery module and the battery pack include the secondary battery having high capacity, high rate and cycle characteristics, a medium or large-sized device selected from the group consisting of an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, and a power storage system can be used as a power source for

Hereinafter, preferred embodiments are presented to aid understanding of the present invention, but the above embodiments are merely illustrative of the present description, and various changes and modifications are possible within the scope and spirit of the present description. It is obvious to those skilled in the art, Naturally, such variations and modifications fall within the scope of the appended claims.

<Example>

<Manufacture of cathode>

Example 1: Preparation of negative electrode

Si (average particle diameter (D50): 3.5 μm) as a silicon-based active material, first conductive material, second conductive material, and polyacrylamide as a binder in a weight ratio of 70:10:10:10 in distilled water as a solvent for forming a negative electrode slurry was added to prepare a negative electrode slurry (solid content concentration: 25% by weight).

The first conductive material is carbon black C (specific surface area: 58 m ² /g, diameter: 37 nm, volatile matter: 0.01%), and the second conductive material is plate-shaped graphite (specific surface area: 17 m ² /g, average particle diameter (D50) ): 3.5 μm).

As a mixing method, a slurry was prepared by dispersing the first conductive material, the second conductive material, the binder and water at 2500 rpm for 30 min using a homo mixer, and then adding the active material and then dispersing at 2500 rpm for 30 min.

As a negative electrode current collector, both sides of a copper current collector (thickness: 8 μm) were coated with the negative electrode slurry at a loading amount of 85 mg/25 cm ² , rolled, and dried in a vacuum oven at 130° C. for 10 hours to obtain a negative electrode An active material layer (thickness: 33 μm) was formed and used as a negative electrode (thickness of negative electrode: 41 μm, porosity of negative electrode 40.0%).

Example 2: Preparation of negative electrode

In Example 1, after dispersing the first conductive material, the binder, and water at 2500 rpm and 30 min using a homo mixer, a silicon-based active material and plate-like graphite are added, and then dispersed at 2500 rpm and 30 min to form a slurry The negative electrode of Example 2 was prepared in the same manner as in Example 1 except for manufacturing.

Example 3: Preparation of negative electrode

In Example 1, an anode was manufactured in the same manner as in Example 1, except that carbon black C having a functional group content of 0.03% was used as the first conductive material.

Example 4: Preparation of negative electrode

In Example 1, Si (average particle diameter (D50): 3.5 μm) as a silicon-based active material, first conductive material, second conductive material, and polyacrylamide as a binder were used in a ratio of 80:5:5:10 A negative electrode was prepared in the same manner as in Example 1 except for the above.

Comparative Example 1: Preparation of negative electrode

A cathode of Comparative Example 1 was prepared in the same manner as in Example 1, except that carbon black C (specific surface area: 63 m ² /g, diameter: 35 nm, volatile matter: 0.15%) was changed and applied as the first conductive material. .

Comparative Example 2: Preparation of negative electrode

In Example 1, the same method as in Example 1 except that carbon black C (specific surface area: 45 m ² /g, diameter: 30-50 nm, volatile matter: 0.40%) was changed and applied as the first conductive material. A negative electrode of Comparative Example 2 was prepared.

Comparative Example 3: Preparation of negative electrode

In Example 1, the same method as in Example 1 except that carbon black C (specific surface area: 45 m ² /g, diameter: 30-50 nm, volatile matter: 0.05%) was changed and applied as the first conductive material. A negative electrode of Comparative Example 3 was prepared.

Comparative Example 4: Preparation of negative electrode

In Example 1, instead of the second conductive material, a linear conductive material (SWCNT) having a BET specific surface area of 1000 to 1500 m ² /g and an aspect ratio of 10000 or more was used as the third conductive material, and Si as the silicon-based active material. (Average particle diameter (D50): 3.5㎛), in the same manner as in Example 1 except for using polyacrylamide as a first conductive material, a third conductive material, and a binder in a weight ratio of 80:10:0.5:9.5. A negative electrode of Comparative Example 4 was prepared.

Comparative Example 5: Preparation of negative electrode

In Example 1, without using the second conductive material, Si (average particle diameter (D50): 3.5 μm) as a silicon-based active material, polyacrylamide as a first conductive material and a binder in a weight ratio of 70:15:15 A negative electrode of Comparative Example 5 was prepared in the same manner as in Example 1, except that it was used.

Comparative Example 6: Preparation of negative electrode

In Example 1, Si (average particle diameter (D50): 3.5 μm) as a silicon-based active material, the first conductive material, the second conductive material, and polyacrylamide as a binder were used in a weight ratio of 55:15:10:20. A negative electrode of Comparative Example 5 was prepared in the same manner as in Example 1 except for the above.

Comparative Example 7: Preparation of negative electrode

68 parts by weight of artificial graphite of secondary particles having a D50 of 16.7 μm and a tap density of 0.91 g/cc, 7 parts by weight of natural graphite, 10 parts by weight of the first conductive material, 10 parts by weight of the second conductive material, and a binder polymer. A negative electrode slurry was prepared by mixing 4.0 parts by weight of styrene butadiene rubber (SBR) and 1.0 part by weight of carboxymethylcellulose (CMC) and adding water as a dispersion medium. At this time, the solid content of the negative electrode slurry was 49% by weight.

The first conductive material and the second conductive material are the same as the first conductive material and the second conductive material in the first embodiment described above.

As a negative electrode current collector, both sides of a copper current collector (thickness: 8 μm) were coated with the negative electrode slurry at a loading amount of 145 mg/25 cm ² , rolled, and dried in a vacuum oven at 130° C. for 10 hours to obtain a negative electrode An active material layer (thickness: 65 μm) was formed and used as a negative electrode. At this time, the negative electrode of Comparative Example 7 was manufactured to satisfy the same capacity as Example 1, and as a result, the negative electrode active material layer was formed thicker to satisfy the same capacity.

<Manufacture of secondary battery>

LiNi _0.6 Co _0.2 Mn _0.2 O ₂ (average particle diameter (D50): 15㎛) as a cathode active material, carbon black (product name: Super C65, manufacturer: Timcal) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder. A positive electrode slurry was prepared by adding N-methyl-2-pyrrolidone (NMP) as a solvent for forming a positive electrode slurry at a weight ratio of 1.5:1.5 (solid content concentration: 78% by weight).

As a positive electrode current collector, both sides of an aluminum current collector (thickness: 12 μm) were coated with the positive electrode slurry at a loading amount of 537 mg/25 cm ² , rolled, and dried in a vacuum oven at 130° C. for 10 hours to obtain a positive electrode An active material layer (thickness: 65 μm) was formed to prepare a positive electrode (anode thickness: 77 μm, porosity: 26%).

The secondary battery of Example 1 was prepared by injecting an electrolyte through a polyethylene separator interposed between the positive electrode and the negative electrode of Example 1.

The electrolyte is an organic solvent in which fluoroethylene carbonate (FEC) and diethyl carbonate (DMC) are mixed in a volume ratio of 30:70, vinylene carbonate is added in an amount of 3% by weight based on the total weight of the electrolyte, and LiPF as a lithium salt ₆ was added at a concentration of 1M.

Secondary batteries were each manufactured in the same manner as described above, except for using the negative electrodes of Examples and Comparative Examples.

Experimental Example 1: Evaluation of coin half cell capacity retention rate

The capacity retention rate of the secondary batteries prepared in Examples and Comparative Examples was evaluated using an electrochemical charge/discharger.

The number of cycles until the 1st capacity reached 80% was confirmed under the conditions of charging (0.5C CC/CV charging, 0.005V, 0.005C cut) and discharging (0.5C CC discharging, 1.0V cut) of the coin half-cell battery.

The N-th capacity retention rate was evaluated by the following formula. The results are shown in Table 1 below.

Capacity retention rate (%) = {(discharge capacity at the Nth cycle)/(discharge capacity at the first cycle)} Х 100

Number of cycles to maintain 80% capacity Example 1 64 Example 2 71 Example 3 65 Example 4 94 Comparative Example 1 54 Comparative Example 2 41 Comparative Example 3 52 Comparative Example 4 33 Comparative Example 5 29 Comparative Example 6 55 Comparative Example 7 33

As can be seen in Table 1, since Examples 1 to 4 to which carbon black C having a low volatile matter value was applied had a high number of cycles until reaching 80% capacity compared to the comparative example, the counter electrode was a Li metal coin. It was also confirmed that the half-cell lifespan evaluation was effective in maintaining capacity.

For reference, Comparative Examples 1 to 3 are negative electrodes corresponding to cases in which the functional group content of the dotted conductive material is exceeded, and in the case of Comparative Example 4, the dotted conductive material of the present invention is satisfied, but corresponds to a negative electrode to which a linear conductive material is applied instead of a planar conductive material. Comparison Example 5 is a case in which the point-type conductive material of the present invention is applied alone (a planar conductive material is not applied), and in the case of Comparative Example 6, the silicon content is less than the scope of the present application. In addition, Comparative Example 7 corresponds to a case in which a conventional carbon-based negative electrode is applied instead of a silicon-based negative electrode.

In particular, in the case of Comparative Example 7, graphite having a low capacity was prepared to match the same capacity as the silicon-based electrode of Example 1, and thus the thickness of the electrode became very thick, resulting in desorption from the negative electrode current collector layer and increased electrode resistance, resulting in poor performance. It was confirmed that it fell compared to Examples 1 to 4.

Experimental Example 2: Secondary battery life evaluation

Life evaluation was performed on the secondary batteries prepared in Examples and Comparative Examples using an electrochemical charger and discharger, and capacity retention rates were evaluated. The secondary battery is 1) charged (0.33C CC/CV charge 4.2V 0.05C cut) and discharged (0.33C CC discharge 3.0V cut), this is the first cycle, and 2) charge (1.0C CC/CV charge 4.2V) 0.05C cut) and discharge (0.5C CC discharge, 3.0V cut) conditions, the cycle from the second cycle until the capacity retention rate reached 80% was checked to conduct charging and discharging.

The N-th capacity retention rate was evaluated by the following formula. The results are shown in Table 2 below.

Capacity retention rate (%) = {(discharge capacity at the Nth cycle)/(discharge capacity at the first cycle)} Х 100

Number of cycles to maintain 80% capacity Example 1 319 Example 2 328 Example 3 324 Example 4 304 Comparative Example 1 290 Comparative Example 2 271 Comparative Example 3 279 Comparative Example 4 177 Comparative Example 5 156 Comparative Example 6 295 Comparative Example 7 212

As can be seen in Table 2 above, since the number of cycles until 80% capacity is higher in the example in which carbon black C having a low functional group content (Volatile matter) value is applied is higher than in the comparative example, even in a secondary battery using a cathode active material as a counter electrode, the capacity It was found to be effective in maintaining

That is, as can be seen from the above experiment, in the case of the negative electrode composition according to the present invention, in using a silicon-based active material, which is a high-capacity material, to produce a high-capacity battery, the ratio of the aqueous binder is lower than that of the conventional carbon-based negative electrode. As the conductive material, a hydrophobic conductive material having a functional group content (Volatile matter) of 0.01% or more and less than 0.05% can be applied. As a result, the bonding force with the conductive material/binder located nearby is improved, and expansion occurs during charging/discharging of the Si-based negative electrode. However, it was confirmed that the performance was improved by strengthening the bonding in the negative electrode composition.

In Tables 1 and 2, in the case of Comparative Examples 1 to 3, a point-like conductive material having a high functional group content was applied, and there was a problem of side reactions such as gas generation due to the functional group on the surface of the point-like conductive material, indicating that the capacity retention rate and lifespan were reduced. I was able to confirm. In Comparative Examples 4 and 5, the dotted conductive material of the present invention was used, but the planar conductive material was not used (Comparative Example 5) or a combination of linear conductive materials (Comparative Example 4) was used to compensate for the disadvantages of the dotted conductive material. In the absence of a planar conductive material, it was confirmed that the performance was poor despite the advantage of only the linear conductive material. In the case of Comparative Example 6, the content of the silicon-based active material was low, and the lifespan or capacity retention rate was higher than that of other comparative examples, but the content of the silicon-based active material was low, so that high capacity and high energy density could not be formed.

Finally, in the case of Comparative Example 7, graphite with a low capacity was prepared to match the same capacity as the silicon-based electrode of Example 1, and thus the thickness of the electrode became very thick, resulting in detachment from the negative electrode current collector layer and increased electrode resistance. It was confirmed that the performance according to Tables 1 and 2 was lower than that of Examples 1 to 4.

10: negative electrode current collector layer
20: negative electrode active material layer
30: separator
40: positive electrode active material layer
50: positive current collector layer
100: negative electrode for lithium secondary battery
200: positive electrode for lithium secondary battery

Claims (11)

silicon-based active material; cathode conductive material; And a negative electrode composition comprising a negative electrode binder,
The negative electrode conductive material includes a point-shaped conductive material and a plate-shaped conductive material,
The point-like conductive material has a functional group content (Volatile matter) of 0.01% or more and less than 0.05%,
The silicon-based active material is a negative electrode composition of 60 parts by weight or more based on 100 parts by weight of the negative electrode composition. The method of claim 1,
45 to 60 parts by weight of the point-shaped conductive material based on 100 parts by weight of the negative electrode conductive material; and 40 to 55 parts by weight of the plate-shaped conductive material. The method of claim 1,
The anode conductive material is a negative electrode composition of 10 parts by weight or more and 40 parts by weight or less based on 100 parts by weight of the negative electrode composition. The method of claim 1,
The plate-shaped conductive material has a D10 of 0.5 μm or more and 1.5 μm or less, a D50 of 2.5 μm or more and 3.5 μm or less, and a D90 of 7.0 μm or more and 15.0 μm or less. The method of claim 1,
The silicon-based active material is a negative electrode composition comprising at least one selected from the group consisting of SiOx (x = 0), SiOx (0 <x <2), SiC, and Si alloys. The method according to claim 1, wherein the silicon-based active material includes at least one selected from the group consisting of SiOx (x=0), SiOx (0<x<2), and metal impurities, based on 100 parts by weight of the silicon-based active material, the SiOx (x = 0) of a negative electrode composition comprising 70 parts by weight or more. dotted conductive material; and a negative electrode binder to form a mixture;
first mixing by adding water to the mixture; and
A method for producing a negative electrode composition comprising the step of second mixing by adding a silicon-based active material to the mixed mixture,
forming the mixture; Or further comprising a plate-shaped conductive material in the second mixing step,
The point-like conductive material has a functional group content (Volatile matter) of 0.01% or more and less than 0.05%. The method of claim 7, wherein the first mixing and the second mixing are mixing at 2,000 rpm to 3,000 rpm for 10 minutes to 60 minutes. a negative electrode current collector layer; and
an anode active material layer comprising the anode composition according to any one of claims 1 to 6 formed on one or both surfaces of the anode current collector layer;
A negative electrode for a lithium secondary battery comprising a. The method of claim 9,
The thickness of the negative electrode current collector layer is 1 μm or more and 100 μm or less,
A negative electrode for a lithium secondary battery in which the thickness of the negative electrode active material layer is 20 μm or more and 500 μm or less. anode;
A negative electrode for a lithium secondary battery according to claim 9;
a separator provided between the anode and the cathode; and
A lithium secondary battery comprising an electrolyte;

Images